1. Field of the Invention
The invention relates to a displacement transducer that generates an electrical output signal depending on an absolute value of a displacement of a mechanical component or on a displacement change measured by it.
2. Prior Art
It Is known to actuate a changeable electrical resistor via a rod drive for measuring the displacement in connection with mechanical devices. An analog electrical signal corresponding to the displacement distance traveled can be generated by the movement of a wiper over a resistance path.
It is an object of the invention to provide an improved displacement transducer device for measuring an absolute or relative value of a displacement of a mechanical component, such as a brake pedal in a motor vehicle.
According to the invention the displacement transducer for measuring an absolute value of a displacement of a mechanical component or a displacement change of the mechanical component and for generating an electrical output signal according the displacement or the displacement change measured thereby comprises
a magnetic tape having respective magnetic sections with correspondingly changing magnetic polarity, which is connected to the mechanical component so as to move with the mechanical component; and
at least one detection device arranged next to the magnetic tape so that the magnetic tape moves past the at least one detection device in a longitudinal direction thereof; wherein the at least one detection device includes means for detecting the respective magnetic polarity changes as the respective magnetic sections move past the at least one detection device and means for generating the electrical output signal according to the magnetic polarity changes.
In a a first aspect in accordance with the invention, a displacement transducer of the species described at the outset is advantageous in that an electrical output signal is generated by means of a magnetic tape, while detecting polarization changes during a movement of the tape. By means of this a contactless displacement measuring device, which has an extremely small structural size, can be realized in a simple manner.
It is also possible to achieve the detection of longer displacement distances traveled by a mechanical component, for example by the brake pedal of a motor vehicle, in an advantageous manner by the employment of a magnetizable tape, whose length can be easily adapted to the employment conditions, which can be moved past a detection device in its longitudinal direction. In the process, the tape can be magnetized, by means of methods known per se, with respectively changing polarities of predetermined sections for the establishment of individual magnets.
In accordance with a preferred embodiment, the tape is provided with individual magnets on both sides of the sections, which can be respectively moved past a detection device. A higher resolution can be obtained by means of the individual magnets, which are respectively located opposite each other on the sides of the tape, being offset by one-half their length. A displacement transducer has been constructed in this way, by means of which an incremental resolution of the displacement of the tape is possible with half the section width.
In an advantageous manner, the tape in accordance with a further embodiment is made from two partial tapes of a magnetizable and vulcanizable permanently elastic material. During production, a support fabric is vulcanized between the partial tapes in such a way that the tape is flexible in the longitudinal direction and reinforced in a direction vertical thereto. In this way the secure guidance and simple winding of the tape, along with an accurate detection of the displacement distance traveled, is assured even under mechanical stresses.
A simple and compact construction of the displacement transducer is possible in that the one, or respectively two detection devices are built into a measuring cell, wherein the tape can be moved directly past these detection devices. For the assured winding of the tape, spirally shaped guide tracks are provided in the measuring cell, into which the tape can be moved. In addition, in a simple manner the displacement transducer can be directly provided with a printed circuit board, which contains an electrical circuit for the evaluation, further processing and, if required, digitizing of the output signal of the detection devices.
It is also possible for the displacement measurement by means of the displacement transducer in accordance with the invention to employ existing techniques for a contactless, high-resolution detection of the changes in a magnetic field. In this case, a so-called AMR (anisotropic magnetoresistive) measuring element, a GMR (giant magnetoresistive) measuring element, or a Hall measuring element are known as detection devices.
By means of example, in an article in VDI [Association of German Engineers] Report No. 509 (VDI, publishers 1984), pages 263 to 268, entitled xe2x80x9cNeue, alternative Lxc3x6sungen fxc3xcr Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basisxe2x80x9d [Novel, Alternative Solutions for RPM-Sensors on a Magnetoresistive Basis in Motor Vehicles], it is described how a particularly simple and non-sensitive detection of the angle of rotation of a rotating shaft or of gear wheels can be performed with magnetic sensors as measuring elements. This is possible because the direction of the lines of flux of a permanent magnet placed in the sensor can be changed and detected by a movement of the permanent magnet.
Further advantageous embodiments of the invention are recited in the dependent claims.